On Arborescence in Gahnia clarkei and Gahnia sieberiana

Specimens of Gahnia sieberiana from Brisbane, Queensland, andof Gahnia clarkei from near Orbost, Victoria, were collectedand examined both morphologically and anatomically. The speciesgrow in wet areas and are of interest because they representthe largest arborescent species known in the Cyperaceae. Stemdiameters up to 120 mm and stems up to 10 m long have been observed.Such long stems tend to be supported by nearby vegetation. Althoughfresh stems are tough and woody, they are brittle. Branchingof the stems is sympodial, and numerous branches are producedby plants growing in exposed habitats. There is less branchingin plants from shaded habitats. Basal shoots may also occur.Adventitious roots develop basally on most plants, but withG. sieberiana, some adventitious roots form near the shoot apexand grow in and around leaf bases. Anatomical features of interestare an endodermoid layer composed of sclereids with elongate,undulated, outer tangential walls that are lignified and suberized,short vessel elements with horizontal to oblique simple perforationplates, and relatively short sclereids surrounding vessel elementsin the vascular bundles. Some vascular bundles are bipolar.The presence of short vessel elements here is in marked contrastto the longer tracheary elements in other arborescent monocotyledons. Arborescence, stem anatomy, Cyperaceae, Gahnia, saw sedge, Monocotyledon, bipolar bundles, morphology, endodermoid layer